The field of beam scanning for the purpose of gathering information is rapidly advancing. The commercial application and importance of barcode reading is well known and is now becoming more sophisticated with the introduction of two dimensional barcodes. Code 49 is only one example of a new barcode standard that contains information in a two dimensional array. As information density increases, scanning with high speed dense scan patterns becomes necessary in order to read it rapidly.
In addition to barcode reading, the ability to read alphanumeric information is also of great commercial value. Other types of encoded information are being devised, and object recognition requiring scanning readout equipment is also of commercial importance.
The problem of having to orient barcodes with respect to the barcode reading equipment at merchandise check out counters is well known. However, automatic information reading is required in many areas where it may not be convenient for humans to orient the information to be read. Conveyor lines where barcode labels on airline luggage must be read is such an example. Besides the fixed mount scanners found on conveyor lines and under the counter point of sale terminals, portable hand held barcode scanners are also popular today. One common portable scanner which is packaged as a wand of about one half inch in diameter contains a light emitting diode (LED) and photo detector (PD). A hard transparent spherical tip is brought into contact with the barcode to be scanned and smoothly passed across the code. Light transmitted through the spherical tip from the LED is reflected off the bar code creating a modulated reflection which is transmitted back through the tip whereupon it is detected by the PD, and processed as information. The shortcomings of this system are that it requires direct contact with the code, mutual orientation of the code and direction of the stroke across all bars of the code, and a relatively non jerky pass.
Another type of portable scanner uses a laser instead of an LED in order to project a narrow light beam a considerable distance ranging from a few inches to a few feet. In this type of scanner some means of uniformly sweeping the light beam is provided, usually by reflecting it off a moving mirror. Inexpensive small motors have been adapted to oscillate or rotate such mirrors creating a scan in essentially a straight line. Stepper motors have been quite popular for this function but they are prone to causing the beam to move in a jerky fashion (non linear motion). Non linear scanning produces poor decode results.
Some of the best portable laser scanners can read information at distances of several yards and are useful for reading barcode labels where they are out of reach. But again these labels may be affixed with random orientations requiring the user of the scanning equipment to carefully orient and aim the scanner to successfully read them.
In order to read these forms of information it is beneficial to rapidly scan a light beam over the information to be read and at the same time to cover the scan area with a dense scan pattern consisting of many closely spaced scan lines. A scan line typically consists of a fast moving laser generated spot. By scanning at many different angles simultaneously or in rapid succession, the probability of successfully reading randomly oriented coded information is improved so much that the process requires no tedious aiming.
In general, in order to derive information from a scanned object, light is directed at the object, and scanned across it at a known rate. As this light is reflected or scattered back by the object, its intensity will vary when observed from a particular vantage point. This scattered light coming back from the object is essentially amplitude modulated by the absorption and reflection from the surface of the object and thus contains spatial information about the object. This information bearing signal may be detected and decoded or interpreted based upon the known direction and velocity of the scanned spot.
Numerous patents describe methods of generating multiple scan lines of various orientations and kinds but none are known for generating these with only one single optical component such as a mirror and only one moving part. Moreover, most devices for generating scan patterns are best suited for making only one type of pattern and major design modifications are required to make different scan patterns. Furthermore none of the known methods of generating high speed multiple scan lines at significant scan angles achieve this result with a single self-contained miniature low profile component which may be mounted simply with the only alignment required being to reflect a beam off its mirror.
Although some devices use mirrors mounted on a spinning motor as a component to generate beam motion, none are as compact and amenable to packaging in spaces as small as the present invention, nor are any known to be capable of generating such sophisticated scan functions as spinning rasters or spinning lissajous figures for example.
Other scan devices may use numerous holograms on a plate which mimic lenses of various focal lengths to focus a beam at different distances thereby increasing the depth of field of the scanner. At the same time the plate is rotated by a motor which causes the beam to scan. U.S. Pat. No. 4,794,237 describes such a device. U.S. Pat. No. 4,639,070 describes a plurality of rotating holograms, mirrors, prisms and gear systems to achieve scans at various angles and rotations. Separate designs with different multiple combinations of these parts are required to produce different patterns.
In U.S. Pat. No. 4,387,297 individual stepper type motors are used with mirrors attached to their shafts and positioned orthogonally so a laser beam reflects off each mirror in succession making possible the production of a raster pattern or lissajous figures, but these cannot be rotated unless the whole product is rotated.
U.S. Pat. No. 4,797,551 describes a method for producing nine fixed scan lines arranged in groups of three parallel lines at three different angles, but the optical system is complex with many mirrors all carefully aligned with many parts and it is so bulky that it would not be practical for hand held applications.
U.S. Pat. No. 4,041,322 describes the generation of polyphase patterns that look like sinusoidial waves all phase shifted with respect to one another. But this also requires multiple mirrors mounted on a spinning polygon as well as an oscillating mirror. This device cannot rotate the scan patterns nor is it portable enough for convenient hand held applications or mounting in tight spaces.
U.S. Pat. No. 4,794,237 describes a multidirectional holographic scanner which can produce scan lines at many angles. This however requires as many as five mirrors and numerous holograms all mounted on a disk which is rotated by a motor.
U.S. Pat. No. 4,409,469 describes a scanning device which includes a mirror mounted on a wedge. The wedge is spun by a motor causing a beam reflected from it to reflect off multiple mirrors mounted in a circle around the spinning mirror.
None of the known two dimensional scan devices can generate multiple scan lines at different orientations with only one mirror, none are single component items, none have a great palette of possible scan patterns while at the same time are practical to mount in a thin tubular housing small enough to be held in a person's hand and none have a single beam shaping device capable of producing a scanning spot of essentially the same small size over great distances.